1. Field of the Invention
The present invention relates to an actuator latch device of a hard disk drive for locking a magnetic head in a parking area in a magnetic head transfer mechanism of a hard disk drive.
2. Description of the Related Art
A latching mechanism or locking device is typically utilized to prevent undesired movement of the actuator and thus protect the disk from the effects of mechanical shock to the drive. For example, a known magnetic latching mechanism is described in U.S. Pat. No. 5,583,724 to Sung-Wook Kim et al. entitled Magnetic Latching Apparatus For An Actuator Of A Hard Disk Drive. A system using both mechanical and magnetic latching means is described in U.S. Pat. No. 6,088,193 to Nigel F. Misso entitled Pawl Latch For A Disc Drive.
A hard disk drive similar to the U.S. Pat. No. 5,583,724 patent is shown in FIG. 1, and includes a hard disk 20, rotatably installed on a base 10, where a predetermined information is recorded, and a magnetic head transfer mechanism for transferring a magnetic head 50 to a desired track on the hard disk 20 to record or reproduce information. Here, the hard disk is divided into a recording area 22 where information is recorded, and a parking area 21 provided inside the hard disk 20 where the magnetic head 50 safely lands when the rotation of the hard disk 20 stops.
The magnetic head transfer mechanism includes an actuator 30 installed to be capable of pivoting around a pivot shaft 34 provided on the base 10, where the magnetic head 50 is installed, a voice coil motor for pivoting the actuator 30 by means of an electromagnetic force, and a latch device for locking the actuator 30 after the magnetic head 50 safely lands on the parking area 21.
The actuator 30 includes a suspension portion 31 for supporting the magnetic head 50, a arm 32 coupled to the pivot shaft 34 to be capable of pivoting, and a bobbin portion 33 around which a mobile coil 35 of the voice coil motor is wound. The voice coil motor includes the mobile coil 35 wound around the bobbin portion 33, and a magnet 41 attached to a yoke 40 installed on the base 10 for generating a magnetic field. Although not shown in the drawing, a pair of yokes 40 are arranged to face each other from upper and lower sides with respect to the actuator 30. An electromagnetic force is generated by the interaction between the magnetic field generated by the magnet 41 and current flowing through the mobile coil 35. Thus, the actuator 30 pivots in a direction according to the Fleming's left hand rule.
Next, the latch device locks the actuator 30 to prevent movement after the magnetic head 50 safely lands on the parking area 21. The latch device includes a magnetic member 43 installed at the yoke 40 and magnetized by the magnet 41, a damper 60 inserted in a coupling protrusion 36 provided at one end of the bobbin portion 33 of the actuator 30, and an iron piece 61 coupled to one end portion of the damper 60. Thus, when the actuator 30 pivots and the magnetic head 50 installed at the suspension portion 31 moves in the parking area 21 of the hard disk 20, as shown in the drawing, the iron piece 61 coupled to the bobbin portion 33 adheres to the magnetic member 43. Thus, until an electromagnetic force is generated to pivot the actuator 30, the actuator 30 remains in a locked state in which the iron piece 61 and the magnetic member 43 are coupled together by the magnetic force.
The reasons for locking the actuator 30 are as follows. First, the suspension portion 31 for supporting the magnetic head 50 provides an elastic force in a direction in which the magnetic head 50 closely contacts a horizontal surface of the hard disk 20. Accordingly, unless an external force is applied, the magnetic head 50 maintains a state of being in close contact with the horizontal surface of the hard disk 20. However, as the hard disk 20 begins to rotate, flow of air around the magnetic head 50 is generated by the rotation of the hard disk 20. The flow of air generates lift to raise the magnetic head 50 from the horizontal surface of the hard disk 20. Thus, during recording or reproducing information on or from the recording area 22 of the hard disk 20 which is rotating, the magnetic head 50 is raised a predetermined flying height above the horizontal surface of the hard disk 20 in a non-contact state. As long as the magnetic head 50 remains above the surface of the disk 20 scratches are prevented.
However, when the rotation of the hard disk 20 is completely stopped, for example, when the power is turned off, the lift that has raised the magnetic head 50 gradually disappears as the rotation speed of the hard disk 20 decreases and the actuator 30 pivots so that the magnetic head 50 is placed in the parking area 21 before the magnetic head 50 descends and collides with the surface of the hard disk 20. Thus, as the rotation of the hard disk 20 stops and the lift disappears, the magnetic head 50 safely lands on the parking area 21 and the recording area 22 is not contacted by magnetic head 50.
If the magnetic head 50, placed in the parking area 21, was pushed toward the recording area 22 by an external impact, the magnetic head 50 in contact with the surface of hard disk 20 could then come into contact with the recording area 22. Accordingly, a defect such as a scratch can be generated in the recording area 22. Thus, to prevent the above defect, it is desired the actuator 30 be locked when the magnetic head is in the parking area 21 by adopting a latch device so that the actuator 30 does not pivot in response to an external impact.
However, since the actuator 30 is locked by an electromagnetic force applied between the iron piece 61 and the magnetic member 43, if an impact greater than the electromagnetic force is applied, the actuator 30 is unlocked and the magnetic head 50 in contact with the surface of hard disk 20 could then come into contact with the recording area 22.
Also, to pivot the actuator 30, being in a locking state, the electromagnetic force generated between the mobile coil 35 and the magnet 41, which exceeds the coupling force of the magnetic force between the iron piece 61 and the magnetic member 43, is applied to move the actuator 30 to unlock it. Thus, the force to magnetically engage the iron piece 61 and the magnetic member 43 is limited.
That is, when the force to magnetically engage the iron piece 61 and the magnetic member 43 is too small, the actuator 30 is easily unlocked by a small external impact. When the force to magnetically engage the iron piece 61 and the magnetic member 43 is too large, the actuator 30 is not easily unlocked even when the maximum electromagnetic force is generated to pivot the actuator 30. In such a structure, when the actuator 30 is unlocked by overcoming the magnetic engaging force between the iron piece 61 and the magnetic member 43, the actuator 30 springs back abruptly due to inertia and the coupling protrusion 36 may strongly collide with a stopper 42. The use of a stopper is described in the U.S. Pat. No. 6,088,193 patent. If the actuator 30 collides with the stopper 42, head slap may be generated due to the impact. To reduce the head slap, current needs to be applied to the mobile coil 35 to generate a braking force to the actuator 30 at the same time the actuator 30 is unlocked. However, it is difficult to configure a control system to timely applying the needed current to the mobile coil 35 to properly generate the braking force. Also, the damper 60 may be damaged since continuous stress is applied to the damper 60 due to repeated actions of locking and unlocking.
To reduce the above described head slapping, the above system could be modified to reposition the stopper as in U.S. Pat. No. 6,134,086 to Myung-Il Kim and entitled Actuator Crash Stopper For A Hard Disk Drive. However, there remains a problem in determining the proper amount of magnetic force between the iron piece 61 and magnet 43 which should be applied to prevent the actuator 30 from being unlocked by an externally applied force greater that the magnetic force between the iron piece 61 and magnet 43.
Actuator latch devices, incorporated by reference herein, having improved structure for maintaining a locking state of an actuator and for performing electromechanical locking and unlocking actions are described in U.S. Pat. No. 5,381,20 to Chunjer C. Cheng entitled Bi-Stable Mechanical Latch For Disk Drive Actuator; U.S. Pat. No. 5,671,104 to Kohji Takashi et al. entitled System And Method For Locking A Disk Actuator In Vertical And Horizontal Directions; U.S. Pat. No. 5,812,345 to Aaron S. MacPherson et al. entitled Monostable Active Latch For A Disk Drive Actuator; U.S. Pat. No. 5,623,384 to Thomas A. Hickox et al. entitled Landing Zone Inertial Latch; U.S. Pat. No. 5,612,842 to Thomas A. Hickox et al. entitled Landing Zone Inertial Latch; and U.S. Pat. No. 5,483,399 to Woo-Cheol Jeong et al entitled Self-Latching Restraint For An Actuator Of A Disk Drive.